A multiple-input multiple-output (Multi-Input Multi-Output, MIMO) technology, as one of important technologies for improving a peak rate of a user, has currently become important performance of many communications systems, for example, an LTE (Long Term Evolution, long term evolution) system, and a UMTS HSDPA (Universal Mobile Telecommunications System High Speed Downlink Packet Access, universal mobile telecommunications system high speed downlink packet access) system, and the like.
In a UMTS uplink communications system, in order to further improve a peak rate of a user, that is, to double the original 11 Mbps (Mbit/s), a MIMO technology becomes an important solution. In a UMTS system, hybrid automatic repeat request (Hybrid Automatic Repeat ReQuest, HARQ), as a channel encoding technology, can effectively guarantee correct data transmission. The number of HARQ processes is equal to an HARQ round trip time (Hybrid Automatic Repeat reQuest Round Trip Time, HARQ_RTT). When a TTI (Transmission Time Interval, transmission time interval) is 2 ms, HARQ_RTT is equal to 8; and when TTI is 10 ms, HARQ_RTT is equal to 4.
In high-speed uplink packet access (High-Speed Uplink Packet Access, HSUPA) communications, when data transmission in a certain process in a current HARQ_RTT is incorrect, a UE (User Equipment, user equipment) may retransmit the data in a same process in a next HARQ_RTT; and after receiving the retransmitted data, a base station (NodeB) can combine it with the data transmitted last time, thereby improving a data transmission correctness rate.
However, after the MIMO technology is introduced into the HSUPA communications, more than one data stream may be sent at a same time, and whether transmission is correct is mutually independent between two data streams; therefore, an existing HARQ mechanism cannot support data transmission using MIMO. In addition, a rank (rank) in
MIMO is adaptive, that is, a rank value in each scheduling cycle may change. Therefore, when a rank change is combined with HARQ retransmission, how to perform corresponding HARQ processing is still an issue that cannot be resolved by existing solutions.